1. Field of the Invention
The present invention relates to a novel cyclohexanetricarboxylic monoester and its use, more particularly, to a heat-curable resin composition which is suitably applied to coating compositions, adhesives, shaped articles, sealing materials for photosemiconductors and coating liquids for forming protective films of color filters used in liquid crystal displays (LCD), solid-state image sensors such as charge coupled device (CCD), or electroluminescent (EL) devices, etc., and a novel cyclohexanetricarboxylic monoester which is suitable as a curing agent for use in such a heat-curable resin composition.
2. Description of the Prior Art
High luminance blue LED and white LED which have been recently developed have come to find wide applications in backlights for display boards, full color displays and cellular phones, etc. As the sealing materials for photoelectric transducers such as LED, a heat-curable resin composition comprising an epoxy-containing compound and an acid anhydride curing agent has been conventionally used because of its excellent colorless transparency. As the curing agent for epoxy-containing compound used in sealing photoelectric transducers, alicyclic acid anhydrides such as methylhexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride and tetrahydrophthalic anhydride have been generally used.
However, since the above alicyclic acid anhydrides show only a low curing reactivity, a curing accelerator must be additionally used to fully cure heat-curable resin compositions. As such curing accelerators, for example, triphenylphosphonium bromide (JP 2000-344868A), 2-ethyl-4-methylimidazole (JP 2001-114868A), ethylhexane salt of 1,8-diazabicyclo[5.4.0]undecene-7 (JP 2002-97251A), and tetraphenylphosphonium bromide (JP 2003-26763A) have been used.
When using a heat-curable resin composition as the sealing material for blue LED and white LED, the cured product of the heat-curable resin composition is required to retain a good colorless transparency for a long period of time. Under recent tendency toward high luminance and high output of LED, the resin cured product has come to be exposed to high temperatures to cause discoloration (yellowing), this making it difficult to retain a good colorless transparency for a long period of time. The phenyl group or nitrogen component in the curing accelerators is considered as the cause of yellowing of the resin cured product. Therefore, the combined use of the curing accelerator with the sealing epoxy-containing compound is undesirable in view of maintaining a good colorless transparency of the resin cured product while neglecting the improvement of the curability of the epoxy-containing compound.